The Internet of Vehicles is a vehicle interconnect network. A vehicle communications terminal is mounted on each vehicle in the Internet of Vehicles, and inter-vehicle communication is implemented between vehicles by using vehicle communications terminals mounted on the vehicles and by using a mobile communications network, thereby implementing an interconnection between the vehicles. In the United States, a vehicle communications terminal using a DSRC technology is developed, and after vehicle communications terminals using the DSRC technology are mounted on vehicles, wireless communication between the vehicles can be implemented.
A frequency used by the DSRC technology is a spectrum of 5.9 GHz. A characteristic of this spectrum is that for line-of-sight transmission, a receiving correctness rate is high within a data transmission distance range, and for non line of sight, that is, when there is an obstruction, data receiving correctness is poor. Therefore, the DSRC technology can achieve a desirable effect when used in the line of sight within a range of 300 meters.
Services of the Internet of Vehicles are classified into three types. A first type is information entertainment services, where passengers in vehicles can do various entertainment activities by using a communications network. A second type is vehicle efficiency type information services, where the information is released by a road administration department or a participant on a road, and mainly includes information such as road congestion information, road construction information, a speed limit of a road section, weather on a road section, and whether a road is passable. A third type is vehicle safety information, that is, information for avoiding collision, such as a vehicle in front being suddenly stopped, a vehicle in front making a turn, or a vehicle coming from the opposite direction. Information of the first type is generally obtained from the cloud, in communication manners such as 3G and 4G, and a network that covers a wide area needs to be used. For information of the second type, the information may also be released in a same manner as the information of the first type, that is, by using a mobile communications network, or may be released by using a short-range communications technology. When the short-range communications technology is used, road side units (RSU) of a particular density need to be mounted on a road. Because information of the third type is driving information of vehicles, and the vehicles generally move fast, a communication delay needs to be less than 100 ms so as to achieve a collision avoiding effect. Because coverage of a cellular network is too wide, and a link establishment process is relatively complex, it is difficult to ensure a delay. Therefore, a direct vehicle-to-vehicle communication technology, such as the DSRC technology, is suitable for communication to complete information sending of a relatively short distance and a high delay requirement.
Although the DSRC technology is applicable to short-range direct communication transmission, the DSRC technology has extremely serious disadvantages: (1) A frame length of a physical layer of DSRC is variable, and therefore it is impossible to determine available resources, and available resources are reduced when a user sends a large data packet, thereby intensifying contention. (2) A contention process is required each time a vehicle communications terminal sends one data packet, and in a case in which long-term sending or regular sending needs to be performed, not only much time is wasted, but also a quantity of contention times is increased.
For a vehicle safety message that has a high delay requirement, the industry believes that it shall be ensured that a transmission delay is less than 100 ms. An actual link simulation and test result shows that when more than 160 vehicles exist in an area, a transmission delay of a vehicle safety message is far greater than 100 ms.
With respect to deployment and use, the DSRC technology requires RSU deployment, so as to really achieve an objective of intelligent transportation. However, the reality is that neither a vehicle manufacturer nor a road operator is willing to deploy an RSU because the RSU deployment needs to be highly dense, costs of initial mounting and maintenance are huge, and a current profit model seems unclear.
In conclusion, vehicle communications terminals in the prior art use the DSRC technology, and because the frame length of the physical layer of DSRC is variable, resource efficiency is low. In addition, a contention manner causes a transmission delay to fail to meet a requirement for safe vehicle communication in a scenario of highly dense vehicles.